Radiation detector

ABSTRACT

A radiation detector includes a light guide portion optically connecting a first segment positioned closest to the other side in a predetermined direction with a second segment positioned closest to the other side in the predetermined direction.

TECHNICAL FIELD

An aspect of the present invention relates to a radiation detector.

BACKGROUND

A radiation detector which includes a scintillator portion having aplurality of segments, and a light detection unit which detectsscintillation light at a plurality of portions of the scintillatorportion is known (for example, Japanese Unexamined Patent PublicationNo. 2007-93376, Japanese Patent No. 4332613, Japanese Patent No.4338177, Japanese Patent No. 3597979, Japanese Patent No. 3697340,Japanese Patent No. 5013864, and WO 2012/105292 A). In the radiationdetector, the segment which absorbs radiation is specified by thedetection values of the scintillation light at the plurality of portionsof the scintillator portion.

SUMMARY

There is a demand of the radiation detector like described above forease of mounting on an apparatus such as a positron emission tomography(PET) apparatus. In addition, there is also a demand for enhancement ofa characteristic of discrimination between the segments.

An object of an aspect of the present invention is to provide aradiation detector which achieves ease of mounting on an apparatus andhas an enhanced characteristic of discrimination between segments.

According to an aspect of the present invention, a radiation detectorincludes: a first scintillator portion including a plurality of firstsegments arranged along a predetermined direction, and a first opticallydiscontinuous portion provided between the first segments adjacent toeach other; a second scintillator portion including a plurality ofsecond segments arranged along the predetermined direction, and a secondoptically discontinuous portion provided between the second segmentsadjacent to each other; a light detection unit optically connected to afirst end surface of the first segment positioned closest to one side inthe predetermined direction, and a second end surface of the secondsegment positioned closest to the one side in the predetermineddirection; and a light guide portion optically connecting the firstsegment positioned closest to the other side in the predetermineddirection with the second segment positioned closest to the other sidein the predetermined direction. The first segment positioned closest tothe other side in the predetermined direction and the second segmentpositioned closest to the other side in the predetermined direction areoptically coupled to each other. The first segments other than the firstsegment positioned closest to the other side in the predetermineddirection and the second segments other than the second segmentpositioned closest to the other side in the predetermined direction areoptically separated from each other.

In the radiation detector, the light detection unit is opticallyconnected to the first end surface of the first segment positionedclosest to the one side in the predetermined direction, and to thesecond end surface of the second segment positioned closest to the oneside in the predetermined direction. Therefore, electrical connection tothe light detection unit can be performed from the one side in thepredetermined direction, and thus ease of mounting on an apparatus isachieved. In addition, in a case where the surface of the first segmentpositioned closest to the other side in the predetermined direction andthe surface of the second segment positioned closest to the other sidein the predetermined direction are optically coupled to each other by anair layer, an optical coupler, or the like, the passage amount ofscintillation light is limited due to reflection on the coupled portion.Therefore, the separation between the segments in the discriminationcharacteristic is increased, the separation between the other segmentsis reduced, and there is concern that the characteristic ofdiscrimination between the overall segments may be degraded. Contrary tothis, according to the radiation detector, the passage amount ofscintillation light between such segments is increased by the lightguide portion. Therefore, the characteristic of discrimination betweenthe segments can be enhanced.

According to an aspect of the present invention, in the radiationdetector, the light guide portion may be formed by covering a surface ofthe first segment positioned closest to the other side in thepredetermined direction and a surface of the second segment positionedclosest to the other side in the predetermined direction with a lightreflection portion so as to form, a space between the surface of thefirst segment positioned closest to the other side in the predetermineddirection and the surface of the second segment positioned closest tothe other side in the predetermined direction. Accordingly, the lightguide portion is formed by the space and the light reflection portion,and thus the passage amount of scintillation light passing between thefirst segment positioned closest to the other side in the predetermineddirection and the second segment positioned closest to the other side inthe predetermined direction can be increased.

According to an aspect of the present invention, an optical couplingagent provided on the surface of the first segment positioned closest tothe other side in the predetermined direction and on the surface of thesecond segment positioned closest to the other side in the predetermineddirection may be further included, and a refractive index of the opticalcoupling agent may be lower than that of each of the first and secondscintillator portions. Accordingly, the passage amount of scintillationlight between the first segment positioned closest to the other side inthe predetermined direction and the second segment positioned closest tothe other side in the predetermined direction can be further increased.

In addition, in the radiation detector of the present invention, a lightscattering surface formed through laser irradiation may be provided inthe first segment positioned closest to the other side in thepredetermined direction and the second segment positioned closest to theother side in the predetermined direction. Accordingly, the passageamount of the scintillation light passing between the first segmentpositioned closest to the other side in the predetermined direction andthe second segment positioned closest to the other side in thepredetermined direction can be further increased.

According to an aspect of the present invention, in the radiationdetector, a first region including at least a portion of a surface ofthe first segment positioned closest to the one side in thepredetermined direction excluding the first end surface, and a secondregion including at least a portion of a surface of the second segmentpositioned closest to the one side in the predetermined directionexcluding the second end surface, may be formed as diffuse reflectionregions, and a surface of the plurality of first segments other than thefirst end surface and the first region, and a surface of the pluralityof second segments other than the second end surface and the secondregion may be formed as specular reflection regions. The first segmentpositioned closest to the one side in the predetermined direction andthe first segment adjacent to the corresponding first segment havesimilar characteristics of outputs extracted in a case wherescintillation light is generated (the ratio of outputs from both ends),and thus the discrimination therebetween is relatively difficult.Contrary to this, in the radiation detector, since the diffusereflection region is provided on the surface of the first segmentpositioned closest to the one side in the predetermined direction, thecharacteristics of the outputs extracted in a case where scintillationlight is generated (the ratio of outputs from both ends) can bedifferentiated between the corresponding first segment and the firstsegment adjacent to the corresponding first segment. Therefore, thecharacteristic of discrimination between the first segments can beenhanced. Similarly, since the diffuse reflection region is provided onthe surface of the second segment positioned closest to the one side inthe predetermined direction, the characteristic of discriminationbetween the corresponding second segment and the second segment adjacentto the corresponding second segment can be enhanced.

According to an aspect of the present invention, in the radiationdetector, the first region may be formed on one surface of a pair ofsurfaces, which oppose each other, in the first segment positionedclosest to the one side in the predetermined direction, and the secondregion may be formed on one surface of a pair of surfaces, which opposeeach other, in the second segment positioned closest to the one side inthe predetermined direction. In this case, since a plurality of thefirst regions are formed so as to extend in different directions,scintillation light is properly diffused in the first segment positionedclosest to the one side in the predetermined direction. In addition,compared to a configuration in which the first regions are formed onboth of the opposing surfaces, ease of processing is achieved.Similarly, scintillation light is properly diffused in the secondsegment positioned closest to the one side in the predetermineddirection, and compared to a configuration in which the second regionsare formed on both of the opposing surfaces, ease of processing isachieved.

According to an aspect of the present invention, in the radiationdetector, the first region may act as the diffuse reflection region bycovering the surface of the first segment, which is roughened, with alight reflection portion, and the second region may act as the diffusereflection region by covering the surface of the second segment, whichis roughened, with the light reflection portion. The first region mayact as the diffuse reflection region by covering, the surface of thefirst segment with a diffuse reflection portion, and the second regionmay act as the diffuse reflection region by covering the surface of thesecond segment with a diffuse reflection portion. Accordingly, since thefirst region and the second region act as the diffuse reflectionregions, the characteristic of discrimination between the first segmentpositioned closest to the one side in the predetermined direction andthe first segment adjacent to the corresponding first segment can beenhanced.

According to an aspect of the present invention, a light scatteringsurface formed through laser irradiation may be provided in the firstsegment positioned closest to the one side in the predetermineddirection and in the second segment positioned closest to the one sidein the predetermined direction. Accordingly, since the light scatteringsurface is provided in the first segment positioned closest to the oneside in the predetermined direction, the characteristics (the ratio ofoutputs from both ends) of an output extracted in a case wherescintillation light is generated can be differentiated between thecorresponding first segment and the first segment adjacent to thecorresponding first segment. Therefore, the characteristic ofdiscrimination between the first segments can be enhanced. Similarly,since the light scattering surface is provided in the second segmentpositioned closest to the one side in the predetermined direction, thecharacteristic of discrimination between the corresponding secondsegment and the second segment adjacent to the corresponding secondsegment can be enhanced.

According to another aspect of the present invention, a radiationdetector includes: a first scintillator portion including a plurality offirst segments arranged along a predetermined direction, and a firstoptically discontinuous portion provided between the first segmentsadjacent to each other; a second scintillator portion including aplurality of second segments arranged along the predetermined direction,and a second optically discontinuous portion provided between the secondsegments adjacent to each other; and a light detection unit opticallyconnected to a first end surface of the first segment positioned closestto one side in the predetermined direction, and a second end surface ofthe second segment positioned closest to the one side in thepredetermined direction. The first segment positioned closest to theother side in the predetermined direction and the second segmentpositioned closest to the other side in the predetermined direction areoptically connected to each other. The first segments other than thefirst segment positioned closest to the other side in the predetermineddirection and the second segments other than the second segmentpositioned closest to the other side in the predetermined direction areoptically separated from each other. A first region including at least aportion of a surface of the first segment positioned closest to the oneside in the predetermined direction excluding the first end surface, anda second region including at least a portion of a surface of the secondsegment positioned closest to the one side in the predetermineddirection excluding the second end surface, are formed as diffusereflection regions. A surface of the plurality of first segments otherthan the first end surface and the first region, and a surface of theplurality of second segments other than the second end surface and thesecond region are formed as specular reflection regions.

The first segment positioned closest to the one side in thepredetermined direction and the first segment adjacent to thecorresponding first segment have similar characteristics of outputsextracted in a case where scintillation light is generated (the ratio ofoutputs from both ends), and thus the discrimination therebetween isrelatively difficult, Contrary to this, in the radiation detector, sincethe diffuse reflection region is provided on the surface of the firstsegment positioned closest to the one side in the predetermineddirection, the characteristics of the outputs extracted in a case wherescintillation light is generated (the ratio of outputs from both ends)can be differentiated between the corresponding first segment and thefirst segment adjacent to the corresponding first segment. Therefore,the characteristic of discrimination between the first segments can beenhanced. Similarly, since the diffuse reflection region is provided onthe surface of the second segment positioned closest to the one side inthe predetermined direction, the characteristic of discriminationbetween the corresponding second segment and the second segment adjacentto the Corresponding second segment can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a radiation detector of an embodiment ofthe present invention.

FIG. 2 is a sectional view of a radiation detection unit of theradiation detector of FIG. 1.

FIG. 3 is a sectional view of the radiation detector of FIG. 1.

FIG. 4 is a conceptual diagram illustrating a connection state of anoutput extraction portion of FIG. 3.

FIG. 5 is a conceptual diagram illustrating a method of specifying asegment where scintillation light is generated.

FIG. 6 is a schematic view of a PET apparatus on which the radiationdetector of FIG. 1 is mounted.

FIG. 7 is a sectional view of a first modification example of theradiation detector of FIG. 2.

FIG. 8A is a sectional view of a second modification example of theradiation detection unit of FIG. 2, and FIG. 8B is a sectional view of athird modification example of the radiation detection unit of FIG. 2.

FIG. 9 is a sectional view of a fourth modification example of theradiation detection unit of FIG. 2.

FIG. 10 is a sectional view of a fifth modification example of theradiation detector of FIG. 1.

FIGS. 11A and 11B are perspective views of a sixth modification exampleof the radiation detector of FIG. 1.

FIGS. 12A and 12B are sectional views of a seventh modification exampleand an eighth modification example of the radiation detector of FIG. 1.

FIGS. 13A and 13B are sectional views of a ninth modification exampleand a tenth modification example of the radiation detector of FIG. 1.

FIG. 14A is a sectional view of an eleventh modification example of theradiation detector of FIG. 1, and FIG. 14B is a graph illustrating ahistogram of the eleventh modification example.

FIG. 15A is a sectional view of a twelfth modification example of theradiation detector of FIG. 1, and FIG. 15B is a graph illustrating ahistogram of the twelfth modification example.

FIG. 16A is a graph showing a histogram of Comparative Example 1, andFIG. 16B is a graph showing a histogram of Example 1.

FIG. 17A is a graph showing a histogram of Example 2, and FIG. 17B is agraph showing a histogram of Example 3.

FIG. 18A is a sectional view of a radiation detection unit of ReferenceExample, and FIG. 18B is a graph showing a histogram of ReferenceExample.

FIG. 19A is a sectional view of a thirteenth modification example of theradiation detection unit of FIG. 2, and FIG. 19B is a sectional view ofa fourteenth modification example of the radiation detection unit ofFIG. 2.

FIG. 20 is a sectional view of a fifteenth modification example of theradiation detector of FIG. 2.

FIGS. 21A and 21B are sectional views of a sixteenth modificationexample and a seventeenth modification example of the radiation detectorof FIG. 2.

FIG. 22A is a sectional view of an eighteenth modification example ofthe radiation detector of FIG. 2, and FIG. 22B is a sectional view takenalong line B-B of FIG. 22A.

FIG. 23A is a graph showing a histogram of Comparative Example 2, andFIG. 23B is a graph showing a histogram of Example 4.

FIG. 24A is a graph showing a histogram of Example 5, and FIG. 24B is agraph showing a histogram of Example 6.

FIG. 25A is a graph showing a histogram of Example 7, and FIG. 25B is agraph showing a histogram of Example 8.

FIG. 26 is a graph showing a histogram of Example 9.

DETAILED DESCRIPTION

Hereinafter, an embodiment according to the present invention will bedescribed in detail with reference to the drawings. In the followingdescription, like elements which are the same or similar to each otherare denoted by like reference numerals, and overlapping description willnot be repeated.

As illustrated in FIG. 1, a radiation detector 1 includes a plurality ofradiation detection units 10. The plurality of radiation detection units10 are two-dimensionally arranged. In this example, the plurality ofradiation detection units 10 are arranged in a matrix form having fourrows and four columns. The adjacent radiation detection units 10 areintegrated with each other, for example, by adhesion to be fixed to eachother.

As illustrated in FIG. 2, the radiation detection unit 10 includes afirst scintillator portion 20, a second scintillator portion 30, lightreflection portions 50 and 60, and a light detection unit 80. Each ofthe scintillator portions 20 and 30 is formed of a crystal body whichabsorbs radiation; such as gamma rays, that is incident from theoutside, and generates scintillation light. Each of the scintillatorportions 20 and 30 generates scintillation light having an intensitycorresponding to the dose of the absorbed radiation at a position wherethe radiation is absorbed. The crystal body is formed of a crystal suchas Bi₄Ge₃O₁₂ (BGO), Lu₂SiO₅ (LSO) doped with Ce, Lu_(2(1-X))Y_(2X)SiO₅(LYSO), Gd₂SiO₅ (GSO), LuAG (Lu₃Al₅O₁₂) doped with Pr, LaBr₃ (LaBr₃)doped with Ce, LaCl₃ (LaCl₃) doped with Ce, Lu_(0.7)Y_(0.3)AlO₃ (LuYAP)doped with Ce, or lutetium fine silicate (LFS).

The first scintillator portion. 20 has, for example, a regular prismshape. The first scintillator portion 20 includes a plurality of firstsegments 21 arranged along a predetermined direction D, and first lightscattering portions 22 provided between the adjacent first segments 21.That is, the first scintillator portion 20 is divided into the pluralityof (in this example, five) first segments 21 by a plurality of (in thisexample, four) first light scattering portions 22. The first segment 21has, for example, a cubic shape. Hereinafter, the five first segments 21arranged from one side S1 to the other side S2 in the direction D arereferred to as a first segment 21A, a first segment 21B, a first segment21C, a first segment 21D, and a first segment 21E.

The first light scattering portion 22 allows a portion of thescintillation light that is incident onto the corresponding first lightscattering portion 22 to be scattered and thus attenuates the intensityof the scintillation light that passes through the corresponding firstlight scattering portion 22. The first light scattering portion 22 has,for example, a flat surface shape perpendicular to the direction D. Morespecifically, the first light scattering portion 22 has, for example,the same shape (in this example, a square shape) as a first end surface23 of the first segment 21A (a surface on the one side S1 in thedirection D). For example, the plurality of first light scatteringportions 22 are arranged to have the same interval therebetween in thedirection D and overlap each other when viewed in the direction D.

The second scintillator portion 30 has, for example, a regular prismshape. The second scintillator portion 30 includes, a plurality ofsecond segments 31 arranged along the direction D, and second lightscattering portions 32 provided between the adjacent second segments 31.That is, the second scintillator portion 30 is divided into theplurality of (in this example, five) second segments 31 by a pluralityof (in this example, four) second light scattering portions 32. Thesecond segment 31 has, for example, a cubic shape. Hereinafter, the fivesecond segments 31 arranged from the one side S1 to the other side S2 inthe direction D are referred to as a second segment 31A, a secondsegment 31B, a second segment 31C, a second segment 311), and a secondsegment 31E.

The second light scattering portion 32 allows a portion of thescintillation light that is incident onto the corresponding second lightscattering portion 32 to be scattered and thus attenuates the intensityof the scintillation light that passes through the corresponding secondlight scattering portion 32. The second light scattering portion 32 has,for example, a flat surface shape perpendicular to the direction D. Morespecifically, the second light scattering portion 32 has, for example,the same shape (in this example, a square shape) as a second end surface33 of the second segment 31A (a surface on the one side S1 in thedirection D). For example, the plurality of second light scatteringportions 32 are arranged to have the same interval therebetween in thedirection D and overlap each other when viewed in the direction D.

Each of the light scattering portions 22 and 32 is formed by reforming(for example, amorphizing) a portion of the crystal body forming each ofthe scintillator portions 20 and 30. The reforming is performed by laserlight irradiation. More specifically, laser light having alight-transmitting property is focused on the crystal body forming eachof the scintillator portions 20 and 30 and the focal point of the laserlight is relatively moved along a predetermined surface of the crystalbody. Accordingly, light absorption is caused at a portion, in thecrystal body, that is coincident with the focal point of the laser lightsuch that a reformed region is formed along the predetermined surface ofthe crystal body. In a case where the laser light is pulsed laser light,a single reformed spot is formed by the irradiation of a single pulse oflaser light. As a plurality of reformed spots are arranged along thepredetermined surface of the crystal body, a reformed region is formed.The reformed region formed as described above acts as each of the lightscattering portions 22 and 32. That is, each of the light scatteringportions 22 and 32 is formed through laser irradiation.

The reformed spot does not block or absorb scintillation light.Therefore, even when the reformed spot is formed over the entire surfaceof the first light scattering portion 22, a portion of the incidentscintillation light is transmitted. Each of the light scatteringportions 22 and 32 formed as described above has a property of having avarying scintillation light transmittance depending on the angle ofincident of the scintillation light. For example, in a case where thescintillation light is vertically incident onto each of the lightscattering portions 22 and 32, most of the incident scintillation lightis transmitted. On the other hand, as the angle of incidence of thescintillation light is increased, the transmittance is decreasedcompared to a case where the scintillation light is vertically incident.

The first scintillator portion 20 and the second scintillator portion 30configured as described above are arranged so that the first segments21A to 21E and the second segments 31A to 31E are adjacent to each otherand the first light scattering portions 22 and the second lightscattering portions 32 are adjacent to each other in a directionperpendicular to the direction D. In this state, the first segment 21Eand the second segment 31E positioned closest to the other side S2 inthe direction D are optically connected to each other via a connectionportion 40. In this example, a surface 24 of the first segment 21E onthe second scintillator portion 30 side, and a surface 34 of the secondsegment 31E on the first scintillator portion 20 side areroughly-polished surfaces. An optical coupling agent 42 fills a spacebetween the surfaces 24 and 34 and is solidified, thereby the firstsegment 21E and the second segment 31E are bonded to each other andoptically coupled to each other. That is, the first segment 21E and thesecond segment 31E are optically connected to each other between theadjacent boundary surfaces (that is, the surfaces 24 and 34 that faceeach other).

The connection portion 40 is constituted by the surfaces 24 and 34formed as the roughly-polished surfaces, and the optical coupling agent42. By the connection portion 40, scintillation light can be allowed topass between the first segment 21E and the second segment 31E. Even inthe connection portion 40, the surfaces 24 and 34 are formed as theroughly-polished surfaces. Accordingly, compared to a case ofmirror-like surfaces, reflection of the scintillation light that passesthrough the connection portion 40 is suppressed, and the passage amountthereof is increased. As the optical coupling agent 42, for example,room temperature vulcanizing (RTV) rubber, optical grease, silicone oil,or the like can be used.

In the first scintillator portion 20 and the second scintillator portion30, the first segments 21A to 21D excluding the first segment 21E, andthe second segments 31A to 31D excluding the second segment 31E areoptically separated from each other by the light reflection portion 50.The light reflection portion 50 is disposed between the first segments21A to 21D and the second segments 31A to 31D. The light reflectionportion 50 is a film-like reflective member, and comes into contact withthe first segments 21A to 21D and the second segments 31A to 31D. Thesurface of the light reflection portion 50 is a specular reflectionsurface to specularly reflect the scintillation light that is incidentonto the surface. Accordingly, the surfaces (smooth surfaces) of thefirst segments 21A to 21D and the second segments 31A to 31D which comeinto contact with the light reflection portion 50 act as specularreflection regions. The light reflection portion 50 is formed of amaterial such as a Teflon tape (Teflon is a registered trademark),barium sulfate, aluminum oxide, titanium oxide, an enhanced specularreflector (ESR) film, or a polyester film.

The outer surfaces of the first scintillator portion 20 and the secondscintillator portion 30 are covered with the light reflection portion60. The light reflection portion 60 covers, among the outer surfaces ofthe first scintillator portion 20 and the second scintillator portion30, the outer surfaces excluding the first end surface 23 of the firstsegment 21A and the second end surface 33 of the second segment 31A. Thelight reflection portion 60 is a film-like reflective member. The lightreflection portion 60 is separated from the surface 25 of the firstsegment 21E (the surface on the other side S2 in the direction D) andthe surface 35 of the second segment 31E (the surface on the other sideS2 in the direction D), and comes into contact with the outer surfacesexcluding the surfaces 25 and 35. The surface of the light reflectionportion 60 is a specular reflection surface to specularly reflect thescintillation light that is incident onto the surface. Accordingly, thesurfaces of the first segments 21A to 21B and the second segments 31A to31D which come into contact with the light reflection portion 60,excluding a first region 26 and a second region 36 to be describedlater, act as specular reflection regions. The light reflection portion60 is formed of for example, the same material as that of the lightreflection portion 50.

A portion of the surface of the first segment 21A excluding the firstend surface 23, and a portion of the surface of the second segment 31Aexcluding the second end surface 33 are formed as roughly-polishedsurfaces. Accordingly, the first region 26 formed as theroughly-polished surface in the first segment 21A, and the second region36 formed as the roughly-polished surface in the second segment 31A actas diffuse reflection regions due to the contact with the lightreflection portion 60. That is, the first region 26 and the secondregion 36 diffusely reflect the incident scintillation light. In otherwords, the first region 26 acts as the diffuse reflection region bycovering the surface of the first segment 21A, which is roughened, withthe light reflection portion 60. The second region 36 acts as thediffuse reflection region by covering the surface of the second segment31A, which is roughened, with the light reflection portion 60.

The first region 26 is formed on one surface of a pair of surfaces,which oppose each other, in the first segment 21A. The second region 36is formed on one surface of a pair of surfaces, which oppose each other,in the second segment 31A. Specifically, in this example, the firstsegment 21 has two pairs of opposing surfaces on the surfaces other thanthe first end surface 23. The first region 26 is formed on one surfaceof the pair of surfaces such that the first region 26 is formed on theentirety of two adjacent surfaces among the surfaces of the firstsegment 21A excluding the first end surface 23. Similarly, the secondregion 36 is formed on the entirety of two adjacent surfaces among thesurfaces of the second segment 31A excluding the second end surface 33.

The radiation detection unit 10 further includes a light guide portion70 which allows the first segment 21E and the second segment 31E to beoptically connected to each other. In the radiation detection unit 10,one side portion 62 of the light reflection portion 60 extends in thedirection perpendicular to the direction. D, and the one side portion 62is provided between the surfaces 25 and 35 formed as theroughly-polished surfaces with an interval therebetween, thereby formingthe light guide portion 70. Accordingly, an air layer 72 having arectangular parallelepiped shape is formed between the one side portion62 and the surfaces 25 and 35. In other words, the surfaces 25 and 35are covered with the light reflection portion 60 to form a space (theair layer 72) between the surfaces 25 and 35, such that the light guideportion 70 is formed. Even by the light guide portion 70, thescintillation light is allowed to pass between the first segment 21E andthe second segment 31E. Accordingly, compared to a case where only theconnection portion 40 is provided, the passage amount of thescintillation light passing between the first segment 21E and the secondsegment 31E is increased. In addition, the surfaces 25 and 35 are notthe roughly-polished surface but may be specular reflection surfaces.

In the radiation detection unit 10, in a case where any of the firstsegments 21A to 21E and the second segments 31A to 31E absorbs radiationand generates scintillation light, while reflection on the specularreflection regions and the diffuse reflection regions is repeated, aportion of the generated scintillation light reaches the first endsurface 23, and the remainder reaches the second end surface 33. At thistime, the scintillation light is attenuated by the first lightscattering portions 22, the second light scattering portions 32, and theconnection portion 40. Therefore, depending on the segment where thescintillation light is generated among the first segments 21A to 21E andthe second segments 31A to 31E, the ratio of the amounts of the lightthat reaches the first end surface 23 and the second end surface 33 ischanged in stages.

Therefore, for example, by calculating the ratio of the amounts of thelight that reaches the first end surface 23 and the amounts of the lightthat reaches the second end surface 33, that is, by performing centroidcalculation, the first segment 21 or the second segment 31 at which thescintillation light is generated (that is, the first segment 21 or thesecond segment 31, which absorbs radiation) can be specified in theradiation detector 1, the first segment 21 or the second segment 31,which absorbs radiation, among the first segments 21A to 21E and thesecond segments 31A to 31E of the plurality of radiation detection units10 is specified by using the centroid calculation. Otherwise, the firstsegment 21 or the second segment 31 at which the scintillation light isgenerated may be specified by a method other than the centroidcalculation. For example, a maximum likelihood estimation method may beused.

The light detection unit 80 includes a first light detection portion 82and a second light detection portion 84. The first light detectionportion 82 is optically coupled to the first end surface 23 of the firstsegment 21A, for example, via an optical adhesive. The second lightdetection portion 84 is optically coupled to the second end surface 33of the second segment 31A, for example, via an optical adhesive. Thefirst light detection portion 82 detects the intensity of thescintillation light that is incident onto the first end surface 23, andoutputs an electrical signal having a magnitude corresponding to thedetection value. The second light detection portion 84 detects theintensity of the scintillation light that is incident onto the secondend surface 33, and outputs an electrical signal having a magnitudecorresponding to the detection value. Each of the light detectionportions 82 and 84 is, for example, a semiconductor light detector usinga photomultiplier tube, an avalanche photodiode (APD), a multi-pixelphoton counter (MPPC), or the like. Here, the MPPC is a photon-countingdevice including a plurality of APD pixels operating in Geiger mode.

As illustrated in FIG. 3, the radiation detector 1 further includes anoutput extraction portion 90 which extracts an output from the lightdetection unit 80 of each of the radiation detection units 10, and anoperation portion 100 which specifies the generation position of thescintillation light on the basis of the output extracted from the outputextraction portion 90. The output extraction portion 90 is electricallyconnected to each of the radiation detection units 10. The operationportion 100 is electrically connected to the output extraction portion90.

The output extraction portion 90 includes a first resistor chain 92 anda second resistor chain 96. The first light detection portion 82 of eachof the radiation detection units 10 is electrically connected to thefirst resistor chain 92. The second light detection portion 84 of eachof the radiation detection units 10 is electrically connected to thesecond resistor chain 96.

As illustrated in FIG. 4, the positional relationship between the firstlight detection portion 82 and the second light detection portion 84 iscommon to the plurality of radiation detection units 10. That is, in anyof the radiation detection units 10, the first light detection portion82 is positioned on one side (left side in FIG. 4) in a row direction(the direction in which the first scintillator portion 20 and the secondscintillator portion 30 are arranged), and the second light detectionportion 84 is positioned on the other side (right side in FIG. 4) in therow direction.

In the first resistor chain 92, the first light detection portions 82adjacent to each other in the row direction are connected to each othervia a resistor. Furthermore, in the first resistor chain 92, the firstlight detection portions 82 positioned on one side in the row directionare connected to each other via the resistor, and the first lightdetection portions 82 positioned on the other side in the row directionare connected to each other via the resistor. That is, in the firstresistor chain 92, the first light detection portions 82 which areadjacent to each other in the column direction (a directionperpendicular to the row direction on a plane on which the firstscintillator portion 20 and the second scintillator portion 30 arearranged) are connected to each other via the resistor. In the secondresistor chain 96, the second light detection portions 84 adjacent toeach other in the row direction are connected to each other via aresistor. Furthermore, in the second resistor chain 96, the second lightdetection portions 84 positioned on the one side in the row directionare connected to each other via the resistor, and the second lightdetection portions 84 positioned on the other side in the row directionare connected to each other via the resistor. That is, in the secondresistor chain 96, the second light detection portions 84 which areadjacent to each other in the column direction are connected to eachother via the resistor.

To the operation portion 100, electrical signal values at four apexes ofthe first resistor chain 92 are input as outputs A1 to A4, andelectrical signal values at four apexes of the second resistor chain 96are input as outputs B1 to B4.

The operation portion 100 specifies the radiation detection unit 10where scintillation light is generated on the basis of the outputs A1 toA4 and/or the outputs B1 to B4. Furthermore, the operation portion 100specifies the segment where the scintillation light is generated amongthe first segments 21 and the second segments 31 of the specifiedradiation detection unit 10 on the basis of the outputs A1 to A4 and theoutputs B1 to B4. Hereinafter, a method of specifying the segment wherescintillation light is generated will be described.

First, a radiation detector 101 illustrated in FIG. 5 will be described.As illustrated in FIG. 5, the radiation detector 101 includes fourradiation detection units 110. Each of the radiation detection units 110includes six segments 121 (segments 121A to 121F) arranged along a firstdirection d1. The radiation detection units 110 are arranged in a seconddirection d2 that is perpendicular to the first direction d1. Theradiation detection units 110 adjacent to each other in the seconddirection d2 are optically separated from each other by a reflectivemember (not illustrated). In addition, a light scattering portion 122 isformed between the segments 121 adjacent to each other in the firstdirection d1. A first light detection portion 182 is optically connectedto each of the segments 121A, and a second light detection portion 184is optically connected to each of the segments 121F. The first lightdetection portions 182 are connected to the first resistor chain 192,and the second light detection portions 184 are connected to the secondresistor chain 196.

In the radiation detector 101, an operation portion obtains the sum ASof the outputs A1 and A2 at both end portions of the first resistorchain 192, and the ratio R1 of the output A1 (or the difference betweenthe outputs A1 and A2) and the sum AS using the following Expressions(1) and (2). The operation portion specifies the radiation detectionunit 110 where scintillation light is generated, with reference to ahistogram G1 that shows the relationship between the ratio R1 and thecount.AS=A1+A2  (1)R1=A1/AS, or R1=(A1−A2)/AS  (2)

Instead of this or in addition to this, the operation portion may obtainthe sum BS of the outputs B1 and B2 at both end portions of the secondresistor chain 196, and the ratio R2 of the output B1 (or the differencebetween the outputs B1 and B2) and the sum BS using the followingExpressions (3) and (4). In this case, the operation portion may specifythe radiation detection unit 110 where scintillation light is generated,with reference to a histogram G2 that shows the relationship between theratio R2 and the count.BS=B1+B2  (3)R2=B1/BS, or R2(B1−B2)/BS  (4)

Instead of this or in addition to this, the operation portion may obtainthe sum C1 of the outputs A1 and B1, the sum C2 of the outputs A2 andB2, and the sum CS of the outputs C1 and C2, and may obtain the ratio R3of the sum C1 (or the difference between the sum C1 and the sum C2) andthe sum CS. In this case, the operation portion may specify theradiation detection unit 110 where scintillation light is generated,with reference to a histogram (not illustrated) that shows therelationship between the ratio R3 and the count.

That is, the operation portion specifies the radiation detection unit110 where scintillation light is generated, on the basis of the ratio ofone of the outputs A1 and A2 from the first resistor chain 192, and oneof the outputs B1 and B2 from the second resistor chain 196, or theratio of the signal (A1+B1, A2+B2) which is the sum of the signals fromboth sides (that is, the ratio of at least one side).

Subsequently, the operation portion obtains the ratio R4 of the sum AS(or the difference between the sums AS and BS), and the sum of the sumAS and the sum BS using the following Expression (5). The operationportion specifies the segment 121 where scintillation light is generatedamong the plurality of segments 121 of the specified radiation detectionunit 110 with reference to the histogram G3 that represents the ratio R4and the count.R4=AS/(AS+BS), or R4=(AS−BS)/(AS+BS)  (5)

As described above, in the radiation detector 101, the specification ofthe radiation detection unit 110 where scintillation light is generated,and the specification of the segment 121 where scintillation light isgenerated, can be separately performed by the operations based on theoutputs A1 and A2 and the outputs B1 and B2. That is, in each of thefirst direction d1 and the second direction d2, the position where thescintillation light is generated can be independently specified. As aresult, the segment 121 where the scintillation light is generated canbe specified.

By the similar processes as those of the radiation detector 101, in thescintillator portion 1, the operation portion 100 can specify theradiation detection unit 10 where scintillation light is generated onthe basis of the outputs A1 to A4 and/or the outputs B1 and B4. Theoperation portion 100 can specify the segment where scintillation lightis generated among the first segments 21 and the second segments 31 ofthe specified radiation detection unit 10 on the basis of the outputs A1to A4 and the outputs B1 to B4. Otherwise, in the reverse order of theabove-described processing order, the operation portion 100 may specifythe segment where scintillation light is generated among the firstsegments 21 and the second segments 31 of the specified radiationdetection unit 10 on the basis of the outputs A1 to A4 and the outputsB1 to B4, and thereafter specify the radiation detection unit having thespecified segment (that is, the radiation detection unit 10 where thescintillation light is generated).

Next, an example on which the radiation detectors 1 are mounted in anapparatus will be described with reference to FIG. 6. FIG. 6 is aschematic view of a PET apparatus on which the plurality of radiationdetectors 1 are mounted. The plurality of radiation detectors 1 arearranged along the circumference of a circle having a center C as thecenter such that side surfaces 1A on the opposite side of a side onwhich the output extraction portions 90 are provided are directed towardthe center C side of a measurement object. Accordingly, the outputextraction portion 90 of each of the radiation detectors 1 is positionedon the outside in a radial direction of the circle having the center Cas the center. Therefore, electrical connection of the operationportions 100 to the radiation detectors 1 can be performed from theoutside in the radial direction. As described above, in the radiationdetector 1, it becomes possible to easily cope with wiring. Otherwise,the plurality of radiation detectors 1 may also be arranged along thecircumference of the circle having the center C as the center such thatthe side surfaces perpendicular to the direction D are directed towardthe center C side.

Next, operational effects of the radiation detector 1 will be described.

In the radiation detector 1, the light detection unit 80 is opticallyconnected to the first end surface 23 of the first segment 21A and thesecond end surface 33 of the second segment 31A. Therefore, electricalconnection to the light detection unit 80 can be performed from the oneside in the direction D (lower side in FIG. 2), and thus ease ofmounting on an apparatus is achieved in addition, in the radiationdetector 1, the passage amount of scintillation light between the firstsegment 21E and the second segment 31E is increased due to the lightguide portion 70. That is, the light guide portion 70 functions as alight guide. Therefore, the characteristic of discrimination between thesegments can be enhanced.

In the radiation detector 1, the surfaces 25 and 35 are covered with thelight reflection portion 60 to form a space (the air layer 72) betweenthe surfaces 25 and 35, such that the light guide portion 70 is formed.Accordingly, the passage amount of the scintillation light passingbetween the first segment 21E and the second segment 31E can beincreased.

In the radiation detector 1, since the diffuse reflection region isprovided on the surface of the first segment 21A, the characteristics ofan output extracted in a case where scintillation light is generated canbe differentiated between the first segment 21A and the first segment21B. Therefore, the characteristic of discrimination between the firstsegments 21A and 21B can be enhanced. Similarly, since the diffusereflection region is provided on the surface of the second segment 31A,the characteristic of discrimination between the second segments 31A and31B can be enhanced.

In the radiation detector 1, the first region 26 is formed on onesurface of a pair of surfaces, which oppose each other, in the firstsegment 21A, and the second region 36 is formed on one surface of a pairof surfaces, which oppose each other, in the second segment 31A. In thiscase, since a plurality of the first regions 26 are formed so as toextend in different directions, scintillation light is properly diffusedin the first segment 21A. In addition, compared to a configuration inwhich the first regions 26 are formed on both of the opposing surfaces,ease of processing is achieved. Similarly, scintillation light isproperly diffused in the second segment 31A, and compared to aconfiguration in which the second regions 36 are formed on both of theopposing surfaces, ease of processing is achieved.

In the radiation detector 1, by forming the first light scatteringportion 22 between the first segments 21 adjacent to each other throughlaser irradiation, the first scintillator portion 20 is obtained.Similarly, by forming the second light scattering portion 32 between thesecond segments 31 adjacent to each other through laser irradiation, thesecond scintillator portion 30 is obtained. Therefore, for example,compared to a case where a plurality of scintillator blocks are joinedto each other while allowing light scattering members to be interposedtherebetween, the first scintillator portion 20 and the secondscintillator portion 30 can be obtained easily and with high dimensionalaccuracy. As described above, in the radiation detector 1, ease ofmanufacturing and high accuracy are achieved. It is thought that it isnot possible to generally specify the structure or characteristicsregarding the difference between the light scattering portions formedthrough laser irradiation and light scattering portions formed byjoining the plurality of scintillator blocks together while allowing thelight scattering members to be interposed therebetween, through words.In addition, it is thought that it is also not possible or is notpractical to analyze or specify the structure or characteristics on thebasis of measurement.

In the radiation detector 1, by disposing the light reflection portion50 between the first segments 21A to 21D and the second segments 31A to31D, predetermined optical separation can be easily and reliablyrealized.

In the radiation detector 1, between the plurality of radiationdetection units 10, the first light detection portions 82 are connectedto the first resistor chain 92, and the second light detection portions84 are connected to the second resistor chain 96. Therefore, forexample, compared to a case where an output is separately extracted fromeach of a plurality of light detection portions, the number of outputscan be reduced. In addition, by the operations based on the outputs A1to A4 and the outputs B1 to B4 respectively extracted from the firstresistor chain 92 and the second resistor chain 96, the specification ofthe radiation detection unit 10 where scintillation light is generated,and the specification of the first segment 21 or the second segment 31where scintillation light is generated, can be separately performed.Therefore, a good characteristic of discrimination between the segmentscan be ensured while reducing the number of outputs.

In the radiation detector 1, the first scintillator portion 20 and thesecond scintillator portion 30 are arranged so that the first lightscattering portion 22 and the corresponding second light scatteringportion 32 are adjacent to each other in the direction perpendicular tothe direction D. Therefore, when the light scattering portions 22 and 32are formed, laser irradiation can be efficiently performed.

In the radiation detector 1, since the first light detection portions 82having the same positional relationship are connected to the firstresistor chain 92, and the second light detection portions 84 having thesame positional relationship are connected to the second resistor chain96, good discrimination between the segments can be performed by arelatively simple process.

In the radiation detector 1, the operation portion 100 specifies theradiation detection unit 10 where scintillation light is generated onthe basis of at least one of the outputs A1 to A4 from the firstresistor chain 92 and the outputs B1 to B4 from the second resistorchain 96, and specifies the segment where scintillation light isgenerated, among the first segments 21 and the second segments 31 on thebasis of the outputs A1 to A4 and the outputs B1 to B4. By theoperations, the specification of the radiation detection unit 10 wherescintillation light is generated, and the specification of the segmentwhere scintillation light is generated, can be separately performed, andthus a good characteristic of discrimination can be obtained.

In the radiation detector 1, since the plurality of radiation detectionunits 10 are two-dimensionally arranged, the radiation detection rangecan be widened. In addition, even in a case where the plurality ofradiation detection units 10 are two-dimensionally arranged as describedabove, a good characteristic of discrimination between the segments canbe ensured while reducing the number of outputs.

In the radiation detector 1, since the first light scattering portion 22and the second light scattering portion 32 are formed through laserirradiation, the passage amount of scintillation light in each of thelight scattering portions can be easily adjusted by adjusting the areaor formation density of the reformed region of each of the lightscattering portions. Therefore, by increasing the passage amount of thelight scattering portion formed at a position where the passage amountof scintillation light is relatively low, or by decreasing the passageamount of the light scattering portion formed at a position where thepassage amount of scintillation light is relatively high, thecharacteristic of discrimination between the segments can be enhanced.

While the exemplary embodiment of the present invention has beendescribed above, the present invention is not limited to the aboveembodiment and can be modified without departing from the gist describedin the claims or applied to other fields.

For example, as in a radiation detection unit 10A of a firstmodification example illustrated in FIG. 7, the first scintillatorportion 20 and the second scintillator portion 30 may also be formedintegrally with each other. In this case, for example, the firstscintillator portion 20 and the second scintillator portion 30 areformed by being cut from a single scintillator block. In a manufacturingprocess, for example, the boundary between the first segments 21A to 21Dand the second segments 31A to 31D is cut by a dicing saw. In addition,the light reflection portion 50 is inserted between the first segments21A to 21D and the second segments 31A to 31D. In the radiationdetection unit 10A, a light scattering portion 44 formed through laserirradiation is provided instead of the connection portion 40, andaccordingly, the first segment 21E and the second segment 31E aredivided from each other.

Even in the first modification example, as in the above-describedembodiment, ease of mounting on an apparatus can be achieved. Inaddition, according to the first modification example, a process ofbonding the first scintillator portion 20 and the second scintillatorportion 30 to each other is omitted, and thus ease of manufacturing andhigh accuracy can be further achieved. Moreover, since the first segment21E and the second segment 31E are divided from each other by the lightscattering portion 44 formed through laser irradiation, the passageamount of scintillation light between the first segment 21E and thesecond segment 31E can be easily adjusted.

As in a radiation detection unit 10B of a second modification exampleillustrated in FIG. 8A and in a radiation detection unit 10C of a thirdmodification example illustrated in FIG. 8B, the configuration of thelight guide portion 70 may be changed. In the radiation detection unit10B, one side portion 62B of the light reflection portion 60 includes afirst portion 65 and a second portion 66 extending perpendicular to thedirection D. In this example, the extension direction of the firstportion 65 and the extension direction of the second portion 66 areperpendicular to each other. The first portion 65 and the second portion66 are continuous at the tip end portions thereof (end portions on theopposite sides of the surfaces 25 and 35), and the tip end portions arepositioned on the boundary line between the first scintillator portion20 and the second scintillator portion 30. In this example, an air layer72B having a triangular prism shape is formed between the one sideportion 62B and the surfaces 25 and 35. In addition, in the radiationdetection unit 10C, one side portion 62C of the light reflection portion60 has a shape that is curved to be convex toward the opposite side ofthe surfaces 25 and 35 in this example, an air layer 72C having asemicircular prism shape is formed between the one side portion 62C andthe surfaces 25 and 35.

Even in the second and third modification examples described above, asin the above-described embodiment, a good characteristic ofdiscrimination between the segments can be ensured. In addition, in aregion (space) corresponding to the air layers 72, 72B, or 72C, a lightguide member formed of a material that can guide light (for example, amember formed of an acrylic resin and the like) may also be disposed.

As in a radiation detection unit 10D of a fourth modification exampleillustrated in FIG. 9, the configuration of the diffuse reflectionregion may be changed. In the radiation detection unit 10D, the lightreflection portion 60 has diffuse reflection portions 68 that cover thefirst region 26 and the second region 36. The surface of the diffusereflection portion 68 is formed as a diffuse reflection surface. In thiscase, the surfaces corresponding to the first region 26 and the secondregion 36 in the first scintillator portion 20 and the secondscintillator portion 30 do not need to be roughly-polished surface, andthe surfaces may also be smooth surfaces. Even in this configuration,the first region 26 and the second region 36 act as diffuse reflectionregions. That is, in this example, the first region 26 acts as thediffuse reflection region by covering the surface of the first segment21A with the diffuse reflection portion 68, and the second region 36acts as the diffuse reflection region by covering the surface, of thesecond segment 31A with the diffuse reflection portion 68. Therefore,even in the fourth modification example, the characteristic ofdiscrimination, between the second segments 31A and 31B can be enhanced.The first region 26 may be any region as long as the region includes atleast a portion of the surface of the first segment 21A except for thefirst end surface 23. For example, the first region 26 may include thesurface that comes into contact with the light reflection portion 50. Inaddition, the first region 26 may also include a portion of the surfaceof the first segment 21B. Even, in these cases, the characteristic ofdiscrimination between the first segments 21A and 213 can be enhanced.This is applied to the second region 36 in the same manner.

As in a fifth modification example illustrated in FIG. 10, theconfiguration of the output extraction portion 90 may be changed. In thefifth modification example, the positional relationship between thefirst light detection portion 82 and the second light detection portion84 is not common to the plurality of radiation detection units 10. Evenin this case, when the arrangement of the first light detection portions82 and the second light detection portions 84 is known, the segmentwhere light detection unit is generated can be specified by the sameprocess as that described above. Therefore, even in the fifthmodification example, as in the above-described embodiment, ease ofmanufacturing, high accuracy, and ease of mounting on an apparatus areachieved. Furthermore, according to the fifth modification example, evenin a case where scintillation light leaks between the adjacent radiationdetection units 10, an error in the direction position of thescintillation light may be reduced.

A radiation detector 1E and a radiation detection unit 10E may beconfigured as in a sixth modification example illustrated in FIGS. 11Aand 11B. In FIG. 11A, the light reflection portion 60 is not described.In the radiation detector 1E, as illustrated in FIG. 1.1B, a pluralityof the radiation detection units 10E arranged in a matrix form havingfour rows and four columns. As illustrated in FIG. 11A, each of theplurality of radiation detection units 10E is configured by arrangingscintillator portions 20E, which have the same configuration between thefirst scintillator portion 20 and the second scintillator portion 30, ina matrix form having two rows and two columns. The scintillator portions20E adjacent to each other by optically coupled to each other by theconnection portion 40 and are optically separated from each other by thelight reflection portion 50. Each of the radiation detection units 10Eincludes four light detection portions 86A to 86D optically coupled toeach other in the scintillator portion 20E. In FIG. 11B, below theradiation detector 1E, the arrangement of the light detection portions86A to 86D are virtually illustrated by two-dot chain lines. Between theplurality of radiation detection units 10E, the light detection portions86A are connected to a first resistor chain, the light detectionportions 86B are connected to a second resistor chain, the lightdetection portions 86C are connected to a third resistor chain, and thelight detection portions 86D are connected to a fourth resistor chain.Even in the sixth modification example, as in the above-describedembodiment, ease of manufacturing, high accuracy, and ease of mountingon an apparatus are achieved.

The radiation detector 1 may be configured as in a seventh modificationexample illustrated in FIG. 12A. In the seventh modification example,without using the first resistor chain 92 and the second resistor chain96, an output is extracted from each of the first light detectionportions 82 and the second light detection portions 84 of the pluralityof radiation detection units 10. Even in this case, the segment wherescintillation light is generated can be specified by centroidcalculation. Therefore, even in the seventh modification example, as inthe above-described embodiment, ease of manufacturing, high accuracy,and ease of mounting on an apparatus are achieved. Here, theabove-described embodiment is preferable because the number of outputscan be reduced.

The radiation detector 1 may be configured as in an eighth modificationexample illustrated in FIG. 12B. In the eighth modification example, alight detection portion 88 is optically connected to both of the firstend surface 23 of the first segment 21A of one radiation detection unit10 of the radiation detection units 10 adjacent to each other, and thesecond end surface 33 of the second segment 31A of the other radiationdetection unit 10 of the radiation detection units 10 adjacent to eachother. In addition, the light detection portion 88 disposed at the endportion is optically connected only to the first end surface 23 or thesecond end surface 33. The first resistor chain 92 and the secondresistor chain 96 of the radiation detection unit 10 are not used, as inthe seventh, modification example. Even in the eighth modificationexample, as in the above-described embodiment, ease of manufacturing,high accuracy, and ease of mounting on an apparatus are achieved.Furthermore, according to the eighth modification example, by reducingthe number of light detection portions 88, the number of outputs can bereduced.

The radiation detector 1 may be configured as in a ninth modificationexample illustrated in FIG. 13A. A radiation detection unit 10H of theninth modification example is configured such that the firstscintillator portion 20 and the second scintillator portion 30 areoptically connected to each other via two scintillator portions 20Hinterposed therebetween. The two scintillator portions 20H have the sameconfiguration as the first scintillator portion 20 and the secondscintillator portion 30, and are optically coupled to each other via theconnection portion 40 interposed therebetween in the segments positionedclosest to the one side S1 in the direction D. In addition, thescintillator portion 20H adjacent to the first scintillator portion 20is optically coupled to the first segment 21E of the first scintillatorportion 20 via the connection portion 40 interposed therebetween in thesegment positioned closest to the other side S2 in the direction D. Thescintillator portion 20H adjacent to the second scintillator portion 30is optically coupled to the second segment 31E of the secondscintillator portion 30 via the connection portion 40 interposedtherebetween in the segment positioned closest to the other side S2 inthe direction D. That is, the segments of the two scintillator portions20H, which are positioned closest to the one side S1 in the direction D,are optically coupled to each other between the boundary surfacesthereof adjacent to each other (that is, the surfaces that oppose eachother). In addition, the segments and the first and second segments 21Eand 31E are optically coupled to each other between the boundarysurfaces thereof adjacent to each other (that is, the surfaces thatoppose each other). As described above, the first scintillator portion20 and the second scintillator portion 30 may be optically connected toeach other via a plurality of the scintillator portions 20H interposedtherebetween. The first resistor chain 92 and the second resistor chain96 are not used as in the seventh modification example. Even in theninth modification example, as in the above-described embodiment, easeof manufacturing, high accuracy, and ease of mounting on an apparatusare achieved. Furthermore, according to the ninth modification example,by reducing the number of light detection portions 88, the number ofoutputs can be reduced.

As in a tenth modification example illustrated in FIG. 13B, theconfiguration of the light detection unit 80 may be changed. A lightdetection unit 80I of the tenth modification example is configured by aposition detection type light detector capable of detecting a positionwhere scintillation light is detected. As the detector, for example, aposition detection type photomultiplier tube, or a position detectiontype avalanche photodiode may be used. Even in the tenth modificationexample, as in the above-described embodiment, ease of manufacturing,high accuracy, and ease of mounting on an apparatus are achieved.

The radiation detector 1 may be configured as in an eleventhmodification example illustrated in FIG. 14A. In the eleventhmodification example, the first light detection portions 82 and thesecond light detection portions 84 of the plurality of radiationdetection units 10 are connected to a single resistor chain 99. Even inthis case, the segment where scintillation light is generated can bespecified by centroid calculation. Therefore, even in the eleventhmodification example, as in the above-described embodiment, ease ofmanufacturing, high accuracy, and ease of mounting on an apparatus areachieved. In the eleventh modification example, the structure issimplified, and the number of first segments 21 and the number of secondsegments 31 are three. This is applied to a twelfth modificationexample, which will be described below, in the same manner.

The radiation detector 1 may be configured as in the twelfthmodification example illustrated in FIG. 15A. In the twelfthmodification example, as in the eight modification example, the lightdetection portion 88 is optically connected to both of the first endsurface 23 of the first segment 21A of one radiation detection unit 10Kof radiation detection units 10K adjacent to each other, and the secondend surface 33 of the second segment 31A of the other radiationdetection unit 10K of the radiation detection units 10K adjacent to eachother, and the light detection portions 88 are connected to the singleresistor chain 99. In addition, the radiation detection units 10Kadjacent to each other are optically coupled to each other via theconnection portion 40 interposed therebetween in the segments positionedclosest to the one side S1 in the direction D. In addition, the lightreflection portion 60 is common to the radiation detection units 10Kadjacent to each other. Even in the twelfth modification example, as inthe above-described embodiment, ease of manufacturing, high accuracy,and ease of mounting on an apparatus are achieved. Furthermore,according to the twelfth modification example, by reducing the number oflight detection portions 88, the number of outputs can be reduced. Inaddition, as illustrated in FIGS. 14B and 15B, the disparity of thedistribution regarding the separation characteristics that occur betweenthe radiation detection units 10 of the eleventh modification example isreduced in the twelfth modification example, and thus it is seen thatgood separation characteristics are provided. As described above, thetwelfth modification example is preferable even in terms of enhancingthe characteristic of discrimination between the segments.

As in a radiation detection unit 10M of a thirteenth modificationexample illustrated in FIG. 19A, the light guide portion 70 may not beprovided. In the thirteenth modification example, the one side portion62 of the light reflection portion 60 is provided to come into contactwith the surface 25 and the surface 35 formed as the specular reflectionsurfaces. Even in the thirteenth modification example, as in theabove-described embodiment, the diffuse reflection region is provided onthe surface of the first segment 21A, and thus the characteristics ofthe outputs extracted in a case where scintillation light is generatedcan be differentiated between the first segment 21A and the firstsegment 21B. Therefore, the characteristic of discrimination between thefirst segments 21A and 21B can be enhanced. Similarly, since the diffusereflection region is provided on the surface of the second segment 31A,the characteristic of discrimination between the second segments. 31Aand 31B can be enhanced.

As in a radiation detection unit 10N of a fourteenth modificationexample illustrated in FIG. 19B, the first region 26 and the secondregion 36 which act as diffuse reflection regions may not be formed. Inthe fourteenth modification example, the entirety of the surface of thefirst segment 21A and the surface of the second segment 31A are formedas specular reflection regions. Even in the fourteenth modificationexample, as in the above-described embodiment, ease of mounting on anapparatus is achieved, and the characteristic of discrimination betweenthe segments is enhanced.

A radiation detection unit 10P may also be configured as in a fifteenthmodification example illustrated in FIG. 20. In the fifteenthmodification example, a flat light scattering surface 27 is provided inthe first segment 21A. The light scattering surface 27 is disposed alongthe direction D and extends between the first end surface 23 and thefirst light scattering portion 22 between the first segments 21A and21B. The light scattering surface 27 is disposed to pass through thecenter of the first segment 21A. In addition, a flat light scatteringsurface 37 is provided in the second segment 31A. The light scatteringsurface 37 is disposed along the direction D and extends between thesecond end surface 33 and the second light scattering portion 32 betweenthe second segments 31A and 31B, The light scattering surface 37 isdisposed to pass through the center of the second segment 31A. Each ofthe light scattering surfaces 27 and 37 are formed through laserirradiation similar to each of the light scattering portions 22 and 32.

Even in the fifteenth modification example, as in the above-describedembodiment, ease of mounting on an apparatus is achieved, and thecharacteristic of discrimination between the segments is enhanced.Furthermore, since the light scattering surface 27 is provided in thefirst segment 21A, the characteristics of an output extracted in a casewhere scintillation light is generated (the ratio of outputs from bothends) can be differentiated between the first segment 21A and the firstsegment 21B. Therefore, the characteristic of discrimination between thefirst segments 21A and 21B can be enhanced. Similarly, since the lightscattering surfaces 37 is provided in the second segment 31A, thecharacteristic of discrimination between the second segments 31A and 31Bcan be enhanced. In addition, in the fifteenth modification example, thelight scattering surface 27 may not be disposed to pass through thecenter of the first segment 21A and may be disposed at an any position.The light scattering surface 27 may not be disposed along the directionD. A plurality of the light scattering surfaces 27 may be provided inthe first segment 21A. The entirety of the light scattering surfaces 27may be formed as a formation region in which the reformed region isformed, or the light scattering surfaces 27 may also have anon-formation region in which the reformed region is not formed. Thenon-formation region may have, for example, a rectangular shape. In thelight scattering surface 27, the formation region and the non-formationregion may be arranged in a checkered pattern. That is, the formationregion and the non-formation region may each have a rectangular shapeand may be alternately arranged. Otherwise, the formation region and thenon-formation region may be arranged in a stripe pattern. That is, theformation region and the non-formation region may each have a band shapeand may be alternately arranged. These are applied to the lightscattering surface 37 in the same manner.

A radiation detection unit 10Q of a sixteenth modification exampleillustrated in FIG. 21A and a radiation detection unit 10R of aseventeenth modification example illustrated in FIG. 21B may also beconfigured. In the sixteenth modification example, a hemisphericaloptical coupling agent 73 is provided on the surface 25 of the firstsegment 21E, and a hemispherical optical coupling agent 74 is providedon the surface 35 of the second segment 31E. In the seventeenthmodification example, a hemispherical optical coupling agent 75 isprovided on the surface 25 of the first segment 21E and the surface 35of the second segment 31E. The refractive index of the hemisphericaloptical coupling agents 73 to 75 is lower than that of each of the firstand second scintillator portions 20 and 30. As the optical couplingagents 73 to 75, for example, the same material as that of the opticalcoupling agent 42 may be used. The surfaces 25 and 35 are specularreflection surfaces. Even in the sixteenth modification example and theseventeenth modification example, as in the above-described embodiment,ease of mounting on an apparatus is achieved, and the characteristic ofdiscrimination between the segments is enhanced. Furthermore, thepassage amount of scintillation light between the first segment 21E andthe second segment 31E can be further increased. That is, when there isa great difference between the refractive index of each of thescintillator portions 20 and 30 and the refractive index (approximatevalue 1) of the outside thereof (the air layer 72), the scintillationlight that travels through the scintillator portions 20 and 30 is likelyto be totally reflected at the surfaces 25 and 35, respectively, and itbecomes difficult for the scintillation light to exit from each of thescintillator portions 20 and 30. Contrary to this, by providing theoptical coupling agents 73 to 75 having a refractive index between thescintillator portions 20 and 30 and the air layer 72 on the surfaces 25and 35, the scintillation light easily exits from the scintillatorportions 20 and 30 to the air layer 72, and thus the passage amount ofthe scintillation light passing between the first segment 21E and thesecond segment 31E can be further increased. Particularly, in theseventeenth modification example, the optical coupling agent 75functions as a light guide, and thus the passage amount of thescintillation light passing between the first segment 21E and the secondsegment 31E can be further increased. The optical coupling agents 73 to75 may have any shape, and for example, may have a rectangularparallelepiped shape. In addition, the surfaces 25 and 35 may also beroughly-polished surfaces.

A radiation detection unit 10S may be configured as in an eighteenthmodification example illustrated in FIG. 22, In the eighteenthmodification example, a light scattering surface 28 having a flatsurface shape is provided in the first segment 21E. The light scatteringsurface 28 is disposed along the direction D so as to be perpendicularto the surface 24 of the first segment 21E. The light scattering surface28 is disposed to pass through the center of the first segment 21E. Inaddition, a light scattering surface 38 having a flat surface shape isprovided in the second segment 31E. The light scattering surface 38 isdisposed along the direction D so as to be perpendicular to the surface34 of the second segment 31E. The light scattering surface 38 isdisposed to pass through the center of the second segment 31E. Similarto each of the light scattering portions 22 and 32, each of the lightscattering surfaces 28 and 38 is formed through laser irradiation.

Even in the eighteenth modification example, as in the above-describedembodiment, ease of mounting on an apparatus is achieved, and thecharacteristic of discrimination between the segments can be enhanced.Furthermore, the passage amount of the scintillation light passingbetween the first segment 21E and the second segment 31E can be furtherincreased. In addition, in the eighteenth modification example, thelight scattering surface 28 may not be disposed to pass through thecenter of the first segment 21E and may be disposed at an any position.In addition, the light scattering surface 28 may not be disposed alongthe direction D. The plurality of light scattering surfaces 28 may alsobe provided in the first segment 21E. The entirety of the lightscattering surface 28 may have formation regions in which a reformedregion is formed, and the light scattering surface 27 may havenon-formation regions in which a reformed region is not formed. Thenon-formation region may have, for example, a rectangular shape. In thelight scattering surface 28, the formation regions and the non-formationregions may be arranged in a check pattern. That is, the formationregions and the non-formation regions may each have rectangular shapesand may be alternately arranged. Alternatively, the formation regionsand the non-formation regions may be arranged in a stripe pattern. Thatis, the formation regions and the non-formation regions may each haveband shapes and may be alternately arranged. These are applied to thelight scattering surface 38 in the same manner. In addition, the lightguide portion 70 may be further provided.

The first light scattering portion 22 and the second light scatteringportion 32 may not be formed through laser irradiation. For example, thefirst light scattering portion 22 and the second light scatteringportion 32 may be formed by joining a plurality of scintillator blockswhile allowing a light scattering member (optically discontinuousmember) to be interposed therebetween. In this case, the scintillatorblocks act as the first segments 21 and the second segments 31. Inaddition, an optically discontinuous portion may also use refraction orreflection other than scattering described above. The opticallydiscontinuous portion is formed by allowing a medium (opticallydiscontinuous member) having a different refractive index from that ofthe scintillator, for example, air or an optical coupler, to beinterposed between the plurality of scintillator blocks.

EXAMPLES

In Examples and Comparative Example, the characteristic ofdiscrimination between segments in a single radiation detection unit wasexamined. FIG. 16A is a graph showing a histogram of ComparativeExample 1. In Comparative Example 1, each of the first segments 21 andthe second segments 31 are five in number. In addition, as in thefourteenth modification example, the entirety of the surfaces of thefirst segments 21 and the second segments 31 was formed as the specularreflection region. In addition, as in the thirteenth modificationexample, the light guide portion 70 was not provided. The other pointswere the same as those of the above-described embodiment.

As evaluation indices of the discrimination characteristic, an index V1and an index V2 were calculated by the following expressions (6) and(7).V1=(C−B)/(D−A)  (6)V2D−A  (7)

where A represents the position of an apex in a distribution of thefirst segments 21 positioned closest to the one side S1 in the directionD, B represents the position of an apex in a distribution of the firstsegments 21 positioned closest to the other side S2 in the direction D,C represents the position of an apex in a distribution of the secondsegments 31 positioned closest to the other side S2 in the direction D,and D represents the position of an apex in a distribution of the secondsegments 31 positioned closest to the one side S1 in the direction D. Inorder to increase the distance between the distributions and enhance theseparation characteristics, it is preferable that the index V1 isdecreased and the index V s 2 is increased.

As illustrated in FIG. 16A, in Comparative Example 1, the value of theindex V1 was 0.306, and the value of the index V2 was 530.

FIG. 16B is a graph showing a histogram of Example 1. In Example 1, thelight guide portion 70 was provided. The other points were the same asthose of Comparative Example 1 in Example 1, the value of the index V1was 0.255, and the value of the index V2 was 534. As described above,both of the index V1 and the index V2 in Example 1 were enhancedcompared to those of Comparative Example 1. From this, it is seen thatthe characteristic of discrimination between segments can be enhanced byproviding the light guide portion 70.

From FIGS. 16A and 16B, it is seen that in Example 1, compared toComparative Example 1, the distance between the distribution of thefirst segments 21 positioned closest to the other side in the directionD and the distribution of the second segments 31 positioned closest tothe other side in the direction D is reduced. From this, it is seen thatthe characteristic of discrimination between segments can be enhanced byproviding the light guide portion 70.

FIG. 17A is a graph showing a histogram of Example 2. In Example 2, asin the fourth modification example, the first region 26 and the secondregion 36 acted as the diffuse reflection region by providing thediffuse reflection portions 68 using a diffuse reflective material. Theother points were the same as those of Example 1. In Example 2, thevalue of the index V1 was 0.243, and the value of the index V2 was 577.As described above, both of the index V1 and the index V2 were enhancedcompared to those of Example 1. From this, it is seen that thecharacteristic of discrimination between segments can be enhanced byproviding the diffuse reflection regions.

From FIGS. 16B and 17A, it is seen that in Example 2, compared toExample 1, the distance between the distribution of the first segments21 positioned closest to the one side in the direction D and thedistribution of the first segments 21 adjacent to each other on theother side in the direction D with respect to the first segments 21 isincreased. From this, it is seen that the characteristic ofdiscrimination between the first segments 21 can be enhanced by allowingthe first region 26 to act as the diffuse reflection region. Similarly,it is seen that in Example 2, compared to Example 1, the distancebetween the distribution of the second segments 31 adjacent to eachother on the one side in the direction D and the distribution of thesecond segments 31 positioned closest to the other side in the directionD with respect to the second segments 31 is increased. From this, it isseen that the characteristic of discrimination between the secondsegments 31 can be enhanced by allowing the second region 36 to act asthe diffuse reflection region.

FIG. 17B is a graph showing a histogram of Example 3. In Example 3, asin the above-described embodiment, by roughening the first region 26 andthe second region 36 to act as diffuse reflection surfaces, the firstregion 26 and the second region 36 were allowed to act as the diffusereflection regions. The other points were the same as those ofExample 1. In Example 3, the value of the index V1 was 0.228, and thevalue of the index V2 was 641. As described above, both of the index V1and the index V2 were enhanced compared to those of Example 1. Fromthis, it is seen that the characteristic of discrimination betweensegments can be enhanced by providing the diffuse reflection regions. Inaddition, from FIGS. 17B and 18B, it is seen that even in Example 3,compared to Example 1, the distance between the distribution of thefirst segments 21 positioned closest to the one side in the direction Dand the distribution of the first segments 21 adjacent to each other onthe other side in the direction D with respect to the first segments 21is increased. In addition, it is seen that the same is applied to thesecond segment 31.

FIG. 18A is a sectional view of a radiation detection unit 10L ofReference Example. In Reference Example, as in the first modificationexample, by cutting an single scintillator block, the radiationdetection unit 10L including the first scintillator portion 20, thesecond scintillator portion 30, and two scintillator portions 20Loptically connecting the first and second scintillator portions 20 and30 to each other was formed. The first scintillator portion 20, thesecond scintillator portion 30, and the scintillator portions 20L weredivided by light scattering portions 44 formed through laserirradiation. In Reference Example, each of the first segments 21, thesecond segments 31, and segments 21L of the scintillator portion 20Lwere four in number. In addition, the light guide portion 70 was notprovided. The other points were the same as those of the above-describedembodiment. Hereinafter, the first segments 21, the segments 21L, andthe second segments 31 arranged on an optical path from the first lightdetection portion 82 to the second light detection portion 84 arerespectively referred to as a first segment 21 ₁, a first segment 21 ₂,a first segment 21 ₃, a first segment 21 ₄, a segment 21L₅, a segment21L₆, a segment 21L₇, a segment 21L₈, a segment 21L₉, a segment 21L₁₀, asegment 21L₁₁, a segment 21L₁₂, a second segment 31 ₁₃, a second segment31 ₁₄, a second segment 31 ₁₅, and a second segment 31 ₁₆.

In Reference Example, the area of the reformed region in each of thefirst light scattering portion 22 between the first segments 21, and 21₃, the light scattering portion 44 between the first segment 21 ₄ andthe segment 21L₅, a light scattering portion 22L between the segments21L₆ and 21L₇, the light scattering portion 22L between the segments21L₁₀ and 21L₁₁, the light scattering portion 44 between the segment21L₁₂ and the second segment 31 ₁₃, and the second light scatteringportion 32 between the second segments 31 ₁₄ and 31 ₁₅, which are formedat positions where the passage amount of scintillation light wasrelatively high, was reduced compared to those of the other lightscattering portions, such that the passage amount of scintillation lightbetween the segments was limited. In FIG. 19A, the light scatteringportions in which the area of the reformed region was reduced are shownby thick lines. Otherwise, instead of reducing the area of the reformedregion, the passage amount of scintillation light between segments mayalso be limited by reducing the formation density of the reformedregion.

FIG. 18B is a graph showing a histogram of Reference Example.

Reference numerals 1 to 16 in FIG. 18B respectively represent thepositions of apexes of distributions of the first segments 21 ₁ to 21 ₄the segments 21L₅ to 21L₁₂, and the second segments 31 ₁₃ to 31 ₁₆. FromFIG. 18B, it is seen that the distance between the distributions isgreat, and the separation characteristics are good. From this, it isseen that the characteristic of discrimination between segments can beenhanced by limiting the passage amount of scintillation light betweensegments having a relatively high passage amount.

FIG. 23A is a graph showing a histogram of Comparative Example 2. InComparative Example 2, each of the first segments 21 and the secondsegments 31 were seven in number. In addition, as in the fourteenthmodification example, the entirety of the surfaces of the first segments21 and the second segments 31 was formed as the specular reflectionregion. In addition, as in the thirteenth modification example, thelight guide portion 70 was not provided. The other points were the sameas those of the above-described embodiment.

As evaluation indices of the discrimination characteristic, in additionto the index V1 and index V2, an index V(L)/P(L) and an index V(R)/P(R)were calculated. Here, V(L) represents a count in the distribution ofthe first segments 21 which are adjacent to each other on the other sidewith respect to the first segments 21 positioned closest to the one sidein the direction D, P(L) represents a count in the distribution of thefirst segments 21 positioned closest to the one side in the direction D,V(R) represents a count in the distribution of the second segments 31which are adjacent to each other on the other side with respect to thesecond segments 31 positioned closest to the one side in the directionD, and P(R) represents a count in the distribution of the secondsegments 31 positioned closest to the one side in the direction D. Inorder to increase the distance between the distribution of the firstsegments 21 positioned closest to the one side in the direction D andthe distribution of the first segments 21 which are adjacent to eachother on the other side in the direction D with respect to thecorresponding first segments 21 and enhance the separationcharacteristics, it is preferable that V(L)/P(L) is decreased. In orderto increase the distance between the distribution of the second segments31 positioned closest to the one side in the direction D and thedistribution of the second segments 31 which are adjacent to each otheron the other side in the direction D with respect to the correspondingsecond segments 31 and enhance the separation characteristics, it ispreferable that the index V(R)/P(R) is decreased.

As shown in FIG. 23A, in Comparative Example 2, the value of the indexV1 was 0.245, and the value of the index V2 was 753, the value of theindex V(L)/P(L) was 0.204, and the value of the index V(R)/P(R) was0.212.

FIG. 23B is a graph showing a histogram of Example 4. In Example 4, thelight guide portion 70 was provided. The other points were the same asthose of Comparative Example 2. In Example 4, the value of the index V1was 0.152, and the value of the index V2 was 755, the value of the indexV(L)/P(L) was 0.101, and the value of the index V(R)/P(R) was 0.167. Asdescribed above, both of the index V1 and the index V2 in Example 4 wereenhanced compared to those of Comparative Example 2. From this, it isseen that the characteristic of discrimination between segments can beenhanced by providing the light guide portion 70.

From FIGS. 23A and 23B, it is seen that in Example 4, compared toComparative Example 2, the distance between the distribution of thefirst segments 21 positioned closest to the other side in the directionD and the distribution of the second segments 31 positioned closest tothe other side in the direction D is reduced. From this, it is seen thatthe characteristic of discrimination between segments can be enhanced byproviding the light guide portion 70.

FIG. 24A is a graph showing a histogram of Example 5. In Example 5, asin the seventeenth modification example, the hemispherical opticalcoupling agent 73 was provided on the surface of the first segments 21positioned closest to the other side in the direction D and the surfaceof the second segments 31 positioned closest to the other side in thedirection D. The other points were the same as those of Example 4. InExample 5, the value of the index V1 was 0.130, and the value of theindex V2 was 794, the value of the index V(L)/P(L) was 0.179, and thevalue of the index V(R)/P(R) was 0.215. As described above, both of theindex V1 and the index V2 in Example 5 were enhanced compared to thoseof Example 4. From this; it is seen that the characteristic ofdiscrimination between segments can be enhanced by providing the opticalcoupling agent 73.

From FIGS. 23B and 24A, it is seen that in Example 5, compared toExample 4, the distance between the distribution of the first segments21 positioned closest to the other side in the direction D and thedistribution of the second segments 31 positioned closest to the otherside in the direction D is reduced. From this, it is seen that thecharacteristic of discrimination between segments can be enhanced byproviding the optical coupling agent 73.

FIG. 24B is a graph showing a histogram of Example 6. In Example 6, asin the eighteenth modification example, the light scattering surface 28was provided in the first segments 21 positioned closest to the otherside in the direction D, and the light scattering surface 38 wasprovided in the second segments 31 positioned closest to the other sidein the direction D. The other points were the same as those ofComparative Example 2. In Example 6, the value of the index V1 was0.153, and the value of the index V2 was 777, the value of the indexV(L)/P(L) was 0.174, and the value of the index V(R)/P(R) was 0.474. Asdescribed above, both of the index V1 and the index V2 in Example 6 wereenhanced compared to those of Comparative Example 2. From this, it isseen that the characteristic of discrimination between segments can beenhanced by providing the light scattering surfaces 28 and 38.

From FIGS. 23A and 24B, it is seen that in Example 6, compared toExample 2, the distance between the distribution of the first segments21 positioned closest to the other side in the direction D and thedistribution of the second segments 31 positioned closest to the otherside in the direction D is reduced. From this, it is seen that thecharacteristic of discrimination between segments can be enhanced byproviding the light scattering surfaces 28 and 38.

FIG. 25A is a graph showing a histogram of Example 7, In Example 7, asin the fourth modification example, the first region 26 and the secondregion 36 acted as the diffuse reflection region by providing thediffuse reflection portions 68 using a diffuse reflective material. InExample 7, the value of the index V1 was 0.145, and the value of theindex V2 was 792, the value of the index V(L)/P(L) was 0.079, and thevalue of the index V(R)/P(R) was 0.100. As described above, both of theindex V1 and the index V2 were enhanced compared to those of Example 4.From this, it is seen that the characteristic of discrimination betweensegments can be enhanced by providing the diffuse reflection regions.Furthermore, the index V(L)/P(L) was enhanced compared to that ofExample 4. From this, it is seen that the characteristic ofdiscrimination between the first segments 21 positioned closest to theone side in the direction D and the first segments 21 which are adjacentto each other on the other side in the direction D with respect to thecorresponding first segments 21 can be enhanced by providing the diffusereflection regions. In addition, the index V(R)/P(R) was enhancedcompared to that of Example 4. From this, it is seen that thecharacteristic of discrimination between the second segments 31positioned closest to the one side in the direction D and the secondsegments 31 which are adjacent to each other on the other side in thedirection D with respect to the corresponding second segments 31 can beenhanced by providing the diffuse reflection regions.

FIG. 25B is a graph showing a histogram of Example 8. In Example 8, asin the above-described embodiment, by roughening the first region 26 andthe second region 36 to act as diffuse reflection surfaces, the firstregion 26 and the second region 36 were allowed to act as the diffusereflection regions. The other points were the same as those of Example4. In Example 8, the value of the index V1 was 0.136, and the value ofthe index V2 was 771, the value of the index V(L)/P(L) was 0.115, andthe value of the index V(R)/P(R) was 0.139. As described above, both ofthe index V1 and the index V2 were enhanced compared to those of Example4. From this, it is seen that the characteristic of discriminationbetween segments can be enhanced by providing the diffuse reflectionregions. Furthermore, the index V(R)/P(R) was enhanced compared to thatof Example 4. From this, it is seen that the characteristic ofdiscrimination between the second segments 31 positioned closest to theone side in the direction D and the second segments 31 which areadjacent to each other on the other side in the direction D with respectto the corresponding second segments 31 can be enhanced by providing thediffuse reflection regions.

FIG. 26 is a graph showing a histogram of Example 9. In Example 9, as inthe fifteenth modification example, the light scattering surface 27 wasprovided in the first segments 21 positioned closest to the other sidein the direction D, and the light scattering surface 38 was provided inthe second segments 31 positioned closest to the one side in thedirection D. The other points were the same as those of Example 4. InExample 9, the value of the index V1 was 0.144, and the value of theindex V2 was 811, the value of the index V(L)/P(L) was 0.097, and thevalue of the index V(R)/P(R) was 0.112. As described above, both of theindex V1 and the index V2 were enhanced compared to those of Example 4.From this, it is seen that the characteristic of discrimination betweensegments can be enhanced by providing the light scattering surfaces 27and 37. Furthermore, the index V(L)/P(L) was enhanced compared to thatof Example 4. From this, it is seen that the characteristic ofdiscrimination between the first segments 21 positioned closest to theone side in the direction D and the first segments 21 which are adjacentto each other on the other side in the direction D with respect to thecorresponding first segments 21 can be enhanced by, providing the lightscattering surface 27. In addition, the index V(R)/P(R) was enhancedcompared to that of Example 4. From this, it is seen that thecharacteristic of discrimination between the second segments 31positioned closest to the one side in the direction D and the secondsegments 31 which are adjacent to each other on the other side in thedirection D with respect to the corresponding second segments 31 can beenhanced by providing the light scattering surface 37.

According to an aspect of the present invention, a radiation detectorwhich achieves ease of mounting on an apparatus and has an enhancedcharacteristic of discrimination between segments can be provided.

What is claimed is:
 1. A radiation detector comprising: a firstscintillator portion including a plurality of first segments arrangedalong a predetermined direction, and a first optically discontinuousportion provided between the first segments adjacent to each other; asecond scintillator portion including a plurality of second segmentsarranged along the predetermined direction, and a second opticallydiscontinuous portion provided between the second segments adjacent toeach other; a light detection unit optically connected to a first endsurface of the first segment positioned closest to one side in thepredetermined direction, and a second end surface of the second segmentpositioned closest to the one side in the predetermined direction; and alight guide portion optically connecting the first segment positionedclosest to the other side in the predetermined direction with the secondsegment positioned closest to the other side in the predetermineddirection, wherein the first segment positioned closest to the otherside in the predetermined direction and the second segment positionedclosest to the other side in the predetermined direction are opticallycoupled to each other, and the first segments other than the firstsegment positioned closest to the other side in the predetermineddirection and the second segments other than the second segmentpositioned closest to the other side in the predetermined direction areoptically separated from each other.
 2. The radiation detector accordingto claim 1, wherein the light guide portion is formed by covering asurface of the first segment positioned closest to the other side in thepredetermined direction and a surface of the second segment positionedclosest to the other side in the predetermined direction with a lightreflection portion so as to form a space between the surface of thefirst segment positioned closest to the other side in the predetermineddirection and the surface of the second segment positioned closest tothe other side in the predetermined direction.
 3. The radiation detectoraccording to claim 2, further comprising: an optical coupling agentprovided on the surface of the first segment positioned closest to theother side in the predetermined direction and on the surface of thesecond segment positioned closest to the other side in the predetermineddirection, wherein a refractive index of the optical coupling agent islower than that of each of the first and second scintillator portions.4. The radiation detector according to claim 1, wherein a lightscattering surface formed through laser irradiation is provided in thefirst segment positioned closest to the other side in the predetermineddirection and the second segment positioned closest to the other side inthe predetermined direction.
 5. The radiation detector according toclaim 1, wherein a first region including at least a portion of asurface of the first segment positioned closest to the one side in thepredetermined direction excluding the first end surface, and a secondregion including at least a portion of a surface of the second segmentpositioned closest to the one side in the predetermined directionexcluding the second end surface, are formed as diffuse reflectionregions, and a surface of the plurality of first segments other than thefirst end surface and the first region, and a surface of the pluralityof second segments other than the second end surface and the secondregion are formed as specular reflection regions.
 6. The radiationdetector according to claim 5, wherein the first region is formed on onesurface of a pair of surfaces, which oppose each other, in the firstsegment positioned closest to the one side in the predetermineddirection, and the second region is formed on one surface of a pair ofsurfaces, which oppose each other, in the second segment positionedclosest to the one side in the predetermined direction.
 7. The radiationdetector according to claim 5, wherein the first region acts as thediffuse reflection region by covering the surface of the first segment,which is roughened, with a light reflection portion, and the secondregion acts as the diffuse reflection region by covering the surface ofthe second segment, which is roughened, with the light reflectionportion.
 8. The radiation detector according to claim 5, wherein thefirst region acts as the diffuse reflection region by covering thesurface of the first segment with a diffuse reflection portion, and thesecond region acts as the diffuse reflection region by covering thesurface of the second segment with the diffuse reflection portion. 9.The radiation detector according to claim 1, wherein a light scatteringsurface formed through laser irradiation is provided in the firstsegment positioned closest to the one side in the predetermineddirection and in the second segment positioned closest to the one sidein the predetermined direction.
 10. A radiation detector comprising: afirst scintillator portion including a plurality of first segmentsarranged along a predetermined direction, and a first opticallydiscontinuous portion provided between the first segments adjacent toeach other; a second scintillator portion including a plurality ofsecond segments arranged along the predetermined direction, and a secondoptically discontinuous portion provided between the second segmentsadjacent to each other; and a light detection unit optically connectedto a first end surface of the first segment positioned closest to oneside in the predetermined direction, and a second end surface of thesecond segment positioned closest to the one side in the predetermineddirection, wherein the first segment positioned closest to the otherside in the predetermined direction and the second segment positionedclosest to the other side in the predetermined direction are opticallyconnected to each other, the first segments other than the first segmentpositioned closest to the other side in the predetermined direction andthe second segments other than the second segment positioned closest tothe other side in the predetermined direction are optically separatedfrom each other, a first region including at least a portion of asurface of the first segment positioned closest to the one side in thepredetermined direction excluding the first end surface, and a secondregion including at least a portion of a surface of the second segmentpositioned closest to the one side in the predetermined directionexcluding the second end surface, are formed as diffuse reflectionregions, and a surface of the plurality of first segments other than thefirst end surface and the first region, and a surface of the pluralityof second segments other than the second end surface and the secondregion are formed as specular reflection regions.